How can I use a subsurf modifier to make a rounded rectangle for this USB cord?

I found a USB cord that I wanted to model, and I tried to use a subsurf modifier to handle the smooth edges that it has. I made the shape of the body, but I don’t know how to shape one of the ends (usb_test,1.blend (448 KB)). It’s a “rounded rectangle”, like the shape of a running track. I tried adding some loop cuts at the end; it made the shape I wanted, but the other end that’s supposed to be a circle is now some sort of ellipse usb_test,2.blend (450 KB). What can I do to get the rounded rectangle shape I want while keeping the circle shape on the other end?

Something like this?


usb.blend (420 KB)

Ya, that’s it! How did you do it? Did you start with a cube, or a circle, or something like that?